I don't see a check valve called out in the power steering lines. Maybe you can ID it by part number from this page of the parts book. The part number will help your search for one most places, on line, or at salvage yards.
If it is not on this page you can go to https://apb.agcocorp.com/ and use the view books tab to search for the D14 book and find the right drawing.
If this site can't help you with one, Sandy Lake Implement is a good source for hard to find AC parts.